Images as Planes, can not see the image on the plane
Blender does not support .GIF files you could e.g. export to .PNG from Gimp (PNG has also lossless compression and transparency) For all available formats see Formats.

The easiest way is to enable the Import Images as Planes addon. You find it in the menu: File / User Preferences. 



After enabling use File / Import / Images as Planes

To see the texture you need to set the viewports shading mode to Texture:



Behind the scenes the addon has created a plane added a material with an image texture you can check this in the materials properties:



Note: For best performance the dimension of a texture should be a power of 2 (128x128px, 256x256px etc.)